SPONGE-IRON POWDER

Abstract: The invention relates to a composition and a method for producing a finely ground powder of sponge-iron and hard-phase material.

Description: SPONGE-IRON POWDER The present invention relates to iron-based powder compositions containing hard-phase material. More spe- cifically, the invention relates to powder compositions based on sponge iron. According to the invention, a finely divided powder material is prepared which can be used for making com¬ pacted and sintered products. The desired properties of the finished product are determined e.g. by the hard-phase materials selected. The properties of the sintered product can also be affected by alloying additivies which may be included in the powder composition of the invention. Iron-based powder materials containing hard-phase material are described e.g. in an article by Thϋmmler et al (Powder Metallurgy International, Vol. 23, No. 5, 1991, pp 285-290). For making such iron-based materials, the iron-containing starting material used has been atomised iron powder or carbonyl iron which when ground with hard- phase material is stated to provide a mechanically alloyed powder that can be used for making sintered products hav¬ ing high abrasion resistance. It has now been found that if atomised iron or car¬ bonyl iron is replaced by sponge iron as starting material in grinding together with hard-phase materials, it is pos¬ sible to produce a powder of potentially equally useful properties as the known powder. Apart from the advantage of sponge iron being essentially cheaper than atomised iron and carbonyl iron, the powder composition of the present invention can be produced by significantly less energy-intensive and less complicated grinding procedures than when producing the above-mentioned known powder com¬ positions. In the method of the present invention, sponge-iron powder, powder of hard-phase material and optionally alloying substances are mixed in a milling device, such as a ball mill containing balls of steel or ceramic mate- rial. The mill vessel, containing powder and balls, is filled with liquid, such as heptane, alcohol, cyclohexane or water, and a dispersing agent is also optionally added to the liquid, whereupon the vessel is sealed after it has been filled with nitrogen gas or any other inert gas. The mill vessel is thereafter rotated as long as the desired particle size and particle size distribution is obtained. Examples of other types of milling devices are attrition mills or vibratory mills. Grinding methods of the type used according to the present invention are described in German Patent Publica¬ tion 1,905,764. However, this publication is concerned with the grinding of only a metal, without the addition of hard-phase material, thus yielding a type of particles 3 having a powder density of less than 1 g/cm and a surface 2 area of at least 1 m /g. In the conception of the present invention, it has however been found that if these par¬ ticles are mixed with particles of hard-phase material, a powder of inadequate compressibility is obtained. If, on the other hand, grinding of sponge-iron powder takes place in the presence of hard-phase powder, a fine powder is obtained which, optionally after conventional agglomera¬ tion, is well suited for the production of compacted and sintered products, which are expected to have desirable properties because of the presence of hard-phase material. Also in respect of the sintering process itself, the new powders are expected to yield valuable advantages as com¬ pared with conventional powder compositions. The sponge-iron powder used as starting material suitably is a commercially available, annealed or non- annealed sponge-iron powder, such as NC 100.24 or M 100 having an average particle size of 90 μm. These powders are commerically available from Hόganas AB. The invention is however not restricted to powders having such average particle sizes but also larger and smaller sizes can be used. The degree of grinding varies depending on the type and the particle size of the starting materials, and is suitably determined in each particular case. When using e.g. NC 100.24 or M 100 having an average particle size of about 90 μm, favourable results have been obtained when grinding to an average particle size of about 60 μm, pre¬ ferably 50 μm. Generally, small particle sizes are advan¬ tageous in terms of sintering, but less advantageous in terms of compressibility. In certain cases, agglomeration of the powder obtained in grinding may be desirable in order to achieve satisfactory compressibility characteris¬ tics. The hard-phase material can be selected from commer¬ cial hard-phase materials such as NbC, TiN, TiC, A1 2 0_, SiC, Cr^C 2 , VC, Mo 2 C, WC, the amount of hard-phase mate¬ rial in the ground composition amounting to at most about 80% by volume. According to the invention, pulverulent alloying additives can also be admixed in the powder composition, either before or after the grinding process. Examples of alloying additives are Ni, Mo, Mn, Cr, Cu, Si, V, Ti, P, Fe 3 P and C. The invention will be illustrated in more detail in the following Example, which is by no means intended to restrict the scope of the invention. Example To a ball mill having a diameter of 210 mm and a length of 250 mm were charged steel balls (12000 g, dia¬ meter 4 mm) as well as 1200 g of a powder mixture con- taining iron powder, hard-phase powder and optionally alloying elements in powder form. The mill was filled with 2000 g of n-heptane and nitrogen gas. Then, the mill was sealed and rotated at a speed of 59 rpm. The following powder mixtures were ground: NC100.24 + 5.4% A1 2 0 3 (10% by volume of A1 2 0 3 ) ASC100.29 + 5.4% A1 2 0 3 (10% by volume of A1 2 0 3 ) NC100.24 + 9.7% NbC (10% by volume of NbC) ASC100.29 + 9.7% NbC (10% by volume of NbC) NC100.24 + 20% INC0123 (Ni) + 5% A1 2 0 3 ASC100.29 + 20% INC0123 (Ni) + 5% A1 2 0 3 NC100.24 + 20% INC0123 (Ni) + 5% A1 2 0 3 + 3.75% Fe g P ASC100.29 + 20% INC0123 (Ni) + 5% A1 2 0 3 + 3.75% Fe 3 P The powder, designated NC100.24, is a sponge-iron powder commerically available from Hoganas AB and having an average particle size of 105 μm. The powder ASC100.29 is an atomised iron powder from Hδganas AB having an average particle size of 105 μm. A1 2°3 an ~ NbC are a< ^ e( as hard-phase material having an average particle size of less than 5 μm. Fe«P having an average particle size of less than 5 μm is added as alloy¬ ing element, like nickel, INC0123, having an average par¬ ticle size of 8 μm. From Figs 1-4 clearly appears that the atomised powder ASC100.29, when blended during grinding with hard- phase material, permits grinding only to a limited extent, and that an increased grinding time does not lead to any corresponding decreased particle size, which is the case if sponge-iron powder NC100.24 according to the invention is used.

Claims: CLAIMS 1. A composition comprising a powder, blended during grinding, of sponge iron and hard-phase material, the con¬ tent of hard-phase material amounting to at most about 80% by volume. 2. A composition as claimed in claim 1, c h a r ¬ a c t e r i s e d in that it contains as hard-phase material NbC, TiN, TiC, A1 2 0 3 , SiC, Cr 3 C 2 , VC, Mo 2 C, WC and/or combinations thereof. 3. A composition as claimed in any one of the pre¬ ceding claims, c h a r a c t e r i s e d in that it contains as alloying additive Ni, Mo, Mn, Cr, Cu, Si, V, Ti, P, Fe^P, C, and/or combinations thereof. 4. A composition as claimed in claims 1-3, c h a r ¬ a c t e r i s e d in that the composition has an average particle size of less than 60 μm, preferably less than 50 μm. 5. A composition as claimed in any one of the pre¬ ceding claims, c h a r a c t e r i s e d in that it is in agglomerated form. 6. A method for producing a composition of a powder, blended during grinding, containing sponge iron and hard- phase material, c h a r a c t e r i s e d by blending sponge-iron powder and a powder of hard-phase material and optional alloying additives in inert atmosphere in a mill¬ ing device containing liquid, grinding the mixture until the desired particle size and particle size distribution have been obtained, and thereafter separating and drying the pulverulent material. 7. A method as claimed in claim 6, c h a r a c ¬ t e r i s e d in that the liquid is heptane, alcohol, cyclohexane or water or mixtures thereof. 8. A method as claimed in any one of claims 6 and 7, c h a r a c t e r i s e d in that grinding is performed in a ball mill in nitrogen atmosphere.

Inventors: LARSSON LARS-ANGSTROM KE, OSTGATHE MICHAEL, THUEMMLER FRITZ, VAENNMAN ERIK, LARSSON, LARS- ANGSTROM KE, OSTGATHE, MICHAEL, THUEMMLER, FRITZ, VAENNMAN, ERIK
Applicants: HOEGANAES AB, LARSSON LARS ANGSTROM KE, OSTGATHE MICHAEL, THUEMMLER FRITZ, VAENNMAN ERIK, LARSSON, LARS- ANGSTROM KE, OSTGATHE, MICHAEL, THUEMMLER, FRITZ, VAENNMAN, ERIK
Application year: 1994
Main classification: B22F1
IPC codes: B22F1, B22F9, C22C1, C22C33